AMD has much cheaper points of entry to ECC.
this hasn't really been true since Haswell. Now even low-end Celerons and Pentiums support it.
It really depends on the tasks if you NEED it... I wouldn't to a byo nas ever again... I would suggest that a lot of workloads don't need it.
That said, the additional cost should be nominal at this point, and I don't quite get why it isn't standard. It's like the coprocessors in the early 90's eventually became a critical integrated piece.
There seems to be plenty of options in the sub-$200 range.